Users of consumer technology and social media reacted quickly after explosions ripped through crowds near the finish line of the Boston Marathon last week, sending out updates and snapping photos and recording videos that officials said would be "critical" pieces of evidence in their investigation into the bombings.

In the hours after two bombs exploded within 100 yards of each other in Boston's Copley Square shortly before 3 p.m. on April 15, the FBI set up a hotline for citizens to use to tell investigators about photos and videos taken in the area at the time of the incident. On Thursday, investigators released surveillance photos of two suspects and asked the public for help identifying them. A massive, sometimes violent, manhunt ensued and continued into the day on Friday.

Early in the investigation, police stressed that photos and videos would be crucial to solving the crime. "It's our intent to go through every frame of every video we have," said Boston Police Commissioner Ed Davis a day after the bombing.

FBI special agent Richard DesLauriers, who leads the investigation, also said last week that "assistance from the public" would be critical.

Investigators were so eager to get smartphone images related to the bombing that Massachusetts State Police detectives were asking passengers checking in for flights at Boston's Logan International Airport if they had pertinent videos or photos.

"They were asking, 'Was anybody there who had any images?' " said Will Stofega, an IDC analyst who was at the airport and was asked about images by investigators.

Jack Gold, an analyst at J.Gold Associates, said collecting and processing bombing-related images amounted to a "truly massive challenge."

While there are software tools galore to help with facial recognition and pattern recognition, "it still comes down to having human eyes sort through sources of interest," Gold said. "Despite our strides in video analysis and image processing, at the end of the day, the systems we have in place are still childish in their abilities compared to humans."

Keith Jones, an independent computer forensics examiner, expected investigators to comb through social networks looking for "online discussions about planning the attack."

Meanwhile, Twitter users near the marathon finish line started tweeting as soon as the bombs exploded, and their actions illustrated both the upside and the downside of the use of social media in emergencies.

For instance, Twitter was a useful communications tool for public authorities like the Boston police and marathon organizers, but many people also used it to spread reports that were questionable or just plain inaccurate.

Social media "cuts both ways," noted Greg Sterling, an analyst at Opus Research. "It allows you to get the information out more quickly, but it can also fan hysteria."

The Boston Police Department's Twitter log showed the positive side of social media. It was updated minute by minute in the aftermath of the bombings, often with instructions to avoid certain areas, or with information about where police officers might be stationed. It was also a source of information on Friday as police warned residents in Boston and surrounding communities to stay indoors as the suspects were sought.

Other social media sites were also useful sources of information. For instance, Google set up a Person Finder, as it did after the Japan earthquake two years ago, to help people connect with friends and loved ones after the incident.

Miners is a reporter for the IDG News Service. Sharon Gaudin contributed to this story.